The present invention relates to an electrically-operated steering lock device.
A conventional electrically-operated steering lock device is so designed that, for locking of a steering shaft of a vehicle, a lock bolt is protruded toward a steering shaft by biasing force of a spring so as to be engaged with a recessed portion of the steering shaft, by which the steering shaft is locked. Further, an electric motor, which is a lock bolt driving device, is rotationally driven so that the lock bolt engaged with the steering shaft is withdrawn from the recessed portion, by which the steering shaft is unlocked.
Then, with the steering shaft in a locked state, while a so-called steering wheel torque is applied to the steering shaft, the lock bolt is burdened with a load in a rotational direction of the steering shaft. As a result of this, engagement between the lock bolt and the recessed portion of the steering shaft becomes tighter, thereby making it more difficult for the lock bolt to be removed from the recessed portion.
Therefore, in such a state, even if the electric motor is rotationally driven, it can occur that the lock bolt will not come out of the recessed portion on account of this load. In this case, after the steering wheel is moved to some extent to release the steering wheel torque, the electric motor is actuated again, thus allowing the lock bolt to come out of the recessed portion. However, for causing the lock bolt to come out of the recessed portion, as shown above, there is a troublesome requirement in that the electric motor is started twice, which can be predicted to lead to a reduction in a service life of the electric motor.
As a countermeasure for this, an electrically-operated steering lock device described in Japanese Patent No. 3174008 (hereinafter, referred to as “Patent Reference 1”) is provided with a locking member for locking a steering shaft, an unlocking spring member for biasing the locking member toward an unlocking position, and a drive member which actuates the locking member toward the unlocking position via the unlocking spring member and which is actuated by an electric motor. In a state that a steering wheel torque is acting on the locking member, a displacement of the drive member by the electric motor is absorbed by the unlocking spring member, so that spring force is accumulated. Then, when the steering wheel torque is released, the locking member is moved to the unlocking position by the accumulated force of the unlocking spring member, by which the steering shaft is unlocked. As a result of this, it is possible to unlock the steering shaft without starting the electric motor twice.
However, with the steering lock device of this Patent Reference 1, there has been a problem in that an operator, in order to release the steering wheel torque, is required to operate the steering shaft each time, which is troublesome.
Further, with the steering lock device this Patent Reference 1, the locking member is protruded toward the steering shaft by biasing force of the spring member so as to be engaged with a locking recess of the steering shaft, by which the steering shaft is locked.
However, with this structure, there is a possibility that the steering shaft might illicitly be unlocked by operating the locking member against the biasing force of the spring member, by a magnet or the like, with an aim of theft.
As a countermeasure for this, it is conceivable that the spring member for biasing the locking member toward the lock position is changed to one of a stronger spring force. However, in such a case, the electric motor to be used for actuating the locking member against the biasing force of the spring member needs to be a large-sized electric motor of large operating torque. This would lead to a problem in that power consumption is increased, and would also cause the electrically-operated steering lock device to be increased in size.
As another prior art, on the other hand, whereas a conventional electrically-operated steering lock device is so designed generally that a lock bolt which is to be engaged with a steering shaft to lock the steering shaft is actuated by driving force of a motor or the like to lock or unlock the steering shaft, an electrically-operated steering lock mechanism described in Japanese Patent Laid-Open Publication No. 2002-234419 (hereinafter, referred to as “Patent Reference 2”) is so designed that a plate cam for moving a lock pin (equivalent to the lock bolt) is driven by a motor to cause a plunger of a solenoid to be protruded into an engagement recessed portion of the plate cam, thereby restraining rotation of the plate cam, so that the motor is prevented from malfunctioning due to electrical noise. Further, for prevention of malfunctions of the solenoid due to electrical noise, power for the solenoid is interrupted in response to operation of a start-up device provided on a vehicle to be controlled by the steering shaft, thereby maintaining the motor in a restrained state by the solenoid.
However, with the steering lock mechanism of this Patent Reference 2, there is a possibility that vibrations of the vehicle due to its running might cause the plunger of the solenoid to be moved, thereby making the motor deregulated. Further, while the plunger of the solenoid is not protruded into the engagement recessed portion of the plate cam, it can occur that power for the solenoid may be interrupted for some reason, thereby putting the motor in an operable state.